The objective of this research program is to determine the characteristics and mechanisms of the regulation of dopamine D-2 receptors. It is crucial that we understand the regulation of D-2 receptors, since idiopathic or drug-induced changes in the density of dopamine receptors are thought to be involved in the pathophysiology or treatment of psychiatric and movement disorders such as schizophrenia, parkinsonism, and tardive dyskinesia. The cloning of a cDNA for the D-2 receptor makes it possible to develop tools that have not been available for the study of D-2 receptor regulation. In particular, cell lines expressing a high density of D-2 receptors are being created by transfecting cells with the cDNA clone, RGB-2. The aim of this proposal is to develop several cell lines derived from various tissues and to use these cells to determine the mechanisms of desensitization and down-regulation of D-2 receptors. To achieve these goals, the following specific objectives will be met. 1) Four new cell lines expressing D-2 receptors will be created by transfecting cells derived from various tissues with either cDNA or genomic DNA encoding the D-2 receptor. 2) Receptors on the cells will be characterized by radioligand binding, by biochemical assays of adenylate cyclase activity, and by photoaffinity labeling and gel electrophoresis. 3) Conditions for treating cells will be optimized by assessing the possibility of growth-dependent changes in D-2 receptor density. 4) Desensitization of D-2 receptors will be evaluated using four measures of rapid desensitization that assess coupling of receptors to G proteins and subcellular localization of the receptors. 5) The effect on the density of D-2 receptors of treating cells with D-2 receptor agonists will be determined. The time course of agonist-induced loss of receptors will be compared to that of desensitization of adenylate cyclase and to the efficacy of the agonist for inhibition of adenylate cyclase. 6) Agonist-induced changes in levels and transcription of D-2 receptor messenger RNA will be quantified by Northern blot analysis and nuclear runoff experiments.